While working on bpftrace support for BTF in modules [1], I noticed that the verifier behaves incorrectly when attaching to fentry of multiple functions of the same name located in different modules (or in vmlinux). The reason for this is that if the target program is not specified, the verifier will search kallsyms for the trampoline address to attach to. The entire kallsyms is always searched, not respecting the module in which the function to attach to is located. This patch fixes the above issue by extracting the module name from the BTF of the attachment target (which must be specified) and by doing the search in kallsyms of the correct module. This also adds a new test in test_progs which tries to attach a program to fentry of two functions of the same name, one located in vmlinux and the other in bpf_testmod. Prior to the fix, the verifier would always use the vmlinux function address for the target trampoline, attempting to create two trampolines for the same address (which is prohibited). [1] https://github.com/iovisor/bpftrace/pull/2315 --- Changes in v4: - reworked module kallsyms lookup approach using existing functions, verifier now calls btf_try_get_module to retrieve the module and find_kallsyms_symbol_value to get the symbol address (suggested by Alexei) - included Jiri Olsa's comments - improved description of the new test and added it as a comment into the test source Changes in v3: - added trivial implementation for kallsyms_lookup_name_in_module() for !CONFIG_MODULES (noticed by test robot, fix suggested by Hao Luo) Changes in v2: - introduced and used more space-efficient kallsyms lookup function, suggested by Jiri Olsa - included Hao Luo's comments Viktor Malik (2): bpf: Fix attaching fentry/fexit/fmod_ret/lsm to modules bpf/selftests: Test fentry attachment to shadowed functions kernel/bpf/verifier.c | 16 ++- net/bpf/test_run.c | 5 + .../selftests/bpf/bpf_testmod/bpf_testmod.c | 6 + .../bpf/prog_tests/module_attach_shadow.c | 131 ++++++++++++++++++ 4 files changed, 157 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/module_attach_shadow.c -- 2.38.1
